Mold knife preservation system and method

ABSTRACT

A system for preserving a cutting knife can include an actuator for moving a first knife from an engaged to a removed position, at which the first knife does not contact a second knife when a first mold half, to which the actuator is connected, and a second mold half, to which the second knife is connected, move from an open to a closed position.

FIELD OF THE INVENTION

The present invention relates to a mold knife preservation system, which can be used in conjunction with a mold system for the formation of objects, and a method. More particularly, the invention relates to using an actuator, a first knife, and a second knife with a first mold half and a second mold half.

DESCRIPTION OF THE RELATED ART

A molding apparatus can form a part by introducing a parison of molding material between mold halves, closing the mold, and separating the parison in the mold from the parison material outside of the mold, for example, separating the parison in the mold from another parison in a following mold. The part formed can be, for example, a container. The parison can be separated by, for example, cutting by mold knives. For example, a first knife can be connected to a first mold half, and a second knife can be connected to a second mold half. The knives can be configured, so that when the mold halves close, the knives slide over each other, trapping and cutting the parison material between them. For example, the first knife can be a cutting knife with a sharp edge for contacting and cutting the parison material. The second knife can be a bed knife, for holding the parison material so that the sharp edge of the cutting knife can cut through the parison material.

It can be important for the mold knives to be sharp, so that the parison is cut cleanly. When a parison is between the mold halves, so that the mold knives contact and cut the parison material when the mold halves close, the parison material, for example, a thermoplastic, can act to lubricate the knives. It is thought that the lubrication by the parison material can prevent the mold knives from coming into contact with each other. Thus a mold knife can contact soft parison material, rather than another mold knife, and retain its sharpness for an extended period of time.

However, the mold halves can close with no parison material between them. This can occur, for example, when the molding apparatus is being tested or calibrated or if there is an interruption in the parison material being supplied to the molding apparatus. In this case, there is no parison material to serve as a lubricant, and the mold knives can contact each other. For example, the mold knives can contact each other when sliding over each other, or, if there is a slight misalignment of the mold knives, impact each other. Contact of one hard mold knife with another hard mold knife can lead to rapid dulling of the sharp surface or surfaces of a mold knife and/or lead to damage of the mold knife.

When the mold knives become dull or damaged, the cutting of the parison by the mold knives can be such that a less than clean cut results; this can result in uncontrolled drop of the part, which can disrupt the molding cycle, for example, the molding cycle of a molding wheel. Therefore, when a mold knife becomes dull or damaged, it must be replaced. Such replacement requires shutting down the molding apparatus. The downtime and resultant interruption of production has a high associated economic cost. Furthermore, the frequent replacement of mold knives increases maintenance costs. The problem of premature dulling or damage of a knife can be a problem in any machine in which knives cut material and the machine is on occasion run without being fed material.

If a molding apparatus is run so that there is always a parison between the mold halves, dulling and wear of mold knives, for example, a cutting knife, is delayed; the parison material is understood to act as a lubricant between, for example, a cutting knife and a bed knife. However, even in such a case, the mold knives do eventually become dull and worn, so that the molding apparatus must be shut down and the mold knives replaced. Eventual dulling or wear of a knife will occur in any machine in which knives cut material.

There thus remains an unmet need for a mold knife preservation system and method to prevent knives from being prematurely dulled by mold closure without the presence of a parison. There further remains an unmet need for a self-sharpening arrangement and method in which a knife is continually sharpened in a mold closure and cutting step, rather than being continually worn in a mold closure and cutting step.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a mold knife preservation system and method to prevent knives from being prematurely dulled by mold closure without the presence of a parison. It is a further object of the present invention to provide a self-sharpening arrangement and method in which a knife is continually sharpened in a mold closure and cutting step, rather than being continually worn in a mold closure and cutting step.

A system for preserving a cutting knife can include a first mold half and a second mold half. An actuator can be connected to the first mold half; and a first knife can be connected to the actuator. A second knife can be connected to the second mold half. The first mold half and the second mold half can have an open position and a closed position. The actuator can move the first knife from an engaged position to a removed position. At the removed position, the first knife does not contact the second knife when the mold halves move from the open position to the closed position.

A system for self-sharpening a cutting knife can include a first mold half and a second mold half. A first knife can be connected to the first mold half, and a second knife can be connected to the second mold half. The first mold half and the second mold half can have an open position and a closed position. The first knife can come into sliding contact with the second knife when the mold halves move from the open position to the closed position. The first knife can be a cutting knife, and the second knife can be a bed knife. The cutting knife can include a cutting edge, and the bed knife can include a sharpening surface.

A method for preserving a cutting knife can include moving a first knife from an engaged position to a removed position. At the removed position, the first knife does not contact a second knife when a first mold half, to which the first knife is connected, and a second mold half, to which the second knife is connected, move from an open position to a closed position.

A method for self-sharpening of a cutting knife can include moving a first mold half connected to a first knife and a second mold half connected to a second knife from an open position to a closed position. The first knife can be a bed knife and the second knife can be a cutting knife. Alternatively, the first knife can be a cutting knife and the second knife can be a bed knife. A cutting edge of the cutting knife can slide along a sharpening surface of the bed knife.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional view of a mold knife preservation system.

FIG. 2 is a side cross-sectional view of a mold knife preservation system.

FIG. 3 is a side cross-sectional view of a mold knife preservation system.

FIG. 4 is a side cross-sectional view of a mold knife preservation system.

FIG. 5 is a side cross-sectional view of a portion of a mold knife preservation system.

FIG. 6 is a side cross-sectional view of a portion of a mold knife preservation system.

FIG. 7 is a top view of a portion of a mold knife preservation system.

FIG. 8 is a top view of a portion of a mold knife preservation system.

FIG. 9 is a side cross-sectional view of a portion of a mold knife preservation system.

FIG. 10 is a side cross-sectional view of a portion of a mold knife preservation system.

FIG. 11 is a side cross-sectional view of a mold knife self-sharpening system.

FIG. 12 is a side cross-sectional view of a mold knife self-sharpening system.

DETAILED DESCRIPTION

Embodiments of the invention are discussed in detail below. In describing embodiments, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected. A person skilled in the relevant art will recognize that other equivalent parts can be employed and other methods developed without parting from the spirit and scope of the invention. All references cited herein are incorporated by reference as if each had been individually incorporated.

An embodiment of a system for preserving a cutting knife can include the following, as shown in FIGS. 1 and 2. The system can include a first mold half 2, of which a portion is shown, and a second mold half 4, of which a portion is shown. An actuator 6 can be connected to the first mold half 2, and a first knife can be connected to the actuator 6. A second knife can be connected to the second mold half 4. The first mold half 2 and the second mold half 4 have an open position for which the first mold half 2 and the second mold half 4 are not in contact, as shown in FIGS. 1 and 2. The first mold half 2 and the second mold half 4 have a closed position for which the first mold half 2 and the second mold half 4 are in contact, or nearly in contact, as shown in FIGS. 3 and 4. The actuator 6 can move the first knife from an engaged position as shown in FIG. 1 to a removed position as shown in FIG. 2. In the engaged position, the first knife contacts, or nearly contacts the second knife when the mold halves 2 and 4 move from the open position, as shown in FIG. 1, to the closed position, as shown in FIG. 3. In the removed position, the first knife does not contact the second knife when the mold halves 2 and 4 move from the open position, as shown in FIG. 2, to the closed position, as shown in FIG. 4. By open position and closed position, the relative positions of a first mold half 2 and a second mold half 4 are described; that is, in moving from the open position to the closed position the first mold half 2 may move, the second mold half 4 may move, or both the mold half 2 and the mold half 4 may move. The first mold half 2 and the second mold half 4 can be components of, for example, a molding apparatus, such as an extrusion blow molding machine. As used in this text, the term “connected” can either mean directly connected, for example, a part A being directly connected to a part B; or the term “connected” can mean indirectly connected, for example, a part A being connected to a part C, with part A being directly connected to a part B and part B being directly connected to a part C.

When parison material is not between the first mold half 2 and the second mold half 4, the first knife can be moved to the removed position, so that the first knife does not contact the second knife, when the first mold half 2 and the second mold half 4 move to the closed position. Because the first knife and the second knife do not contact each other, the sharpness of the first knife and the second knife is preserved and the first knife and the second knife are not prematurely worn.

In an embodiment, not shown in the Figures, the first knife is a bed knife 10 and the second knife is a cutting knife 8. In other embodiments, shown in FIGS. 1-10, the first knife is a cutting knife 8 and the second knife is a bed knife 10.

The system for preserving a cutting knife can be used, for example, with a mold forming apparatus. A parison can be forced between the first mold half 2 and the second mold half 4. The cutting knife 8 can be in the engaged position. When the first mold half 2 and the second mold half 4 close, the cutting knife 8 can move so that a cutting edge 24 of the cutting knife 8 contacts the parison and separates the parison inside the mold from parison material outside the mold. The cutting knife 8 can come into sliding contact with the bed knife 10 to separate the parison inside the mold from parison material outside the mold. Sliding contact between the cutting knife 8 and the bed knife 10 can be useful, for example, if the parison material is resistant to cutting, or tends to form strands. The parison material can include, for example, a thermoplastic, such as polypropylene, high-density polyethylene, or another type of polyethylene. For example, when the parison material is high-density polyethylene, the first knife, e.g., the cutting knife 8, and the second knife, e.g., the bed knife 10, can be positioned so that they have a separation from each other in the range of from about 0.005 to about 0.010 inches when the first knife is in the engaged position and the first mold half 2 and the second mold half 4 are in the closed position. For example, when the parison material is polypropylene, which can have a tendency to smear when cut instead of cutting cleanly, the first knife, e.g., the cutting knife 8, and the second knife, e.g., the bed knife 10, can be positioned so that they have no separation from each other, that is, they are in sliding contact, when the first knife is in the engaged position and the first mold half 2 and the second mold half 4 are in the closed position. The wall of the parison can be formed of a single layer of material, or multiple layers of material.

As shown in FIGS. 5 and 6, the actuator can be a fluid actuator 36, which can include a cylinder 12 capable of admitting a fluid. FIG. 5 is a side cross-section, along section A-A of FIG. 7, of a portion of a system for preserving a cutting knife 8, with the cutting knife 8 in the engaged position, shown in top view in FIG. 7. FIG. 6 is a side cross-section, along section C-C of FIG. 8, of a portion of a system for preserving a cutting knife 8, with the cutting knife 8 in the removed position, shown in top view in FIG. 8. The cylinder 12 can be for fluid coupling to a fluid supply, and the fluid actuator 36 can include a piston 14 within the cylinder 12. The piston 14 can be connected to the cutting knife 8. The piston 14 can be directly connected to the cutting knife 8. Alternatively, the piston 14 can be indirectly connected to the cutting knife 8; for example, the piston 14 can be connected to a rod 30 which can act on a lever 22, the lever 22 can be connected to a knife holder 18, and the knife holder 18 can hold a cutting knife 8, as shown in FIGS. 5 and 6. The fluid which the cylinder 12 can admit, can be a gas, as, for example, in the case of a pneumatic cylinder; alternatively, the fluid can be a liquid, as, for example, in the case of a hydraulic cylinder. In the case of a gaseous fluid, for example, air, nitrogen, or any other gas, the cylinder 12 can be for fluid coupling to a supply of pressurized gas. In the case of a liquid fluid, the cylinder 12 can be for fluid coupling to a supply of pressurized liquid. For example, one hose and one fitting can be fluidly coupled to the cylinder 12 and fluidly coupled to a supply of pressurized air, to supply the cylinder 12 with air.

The system can include an actuator valve fluidly coupled to the cylinder 12 and for fluidly coupling to the fluid supply. The actuator valve can be fluidly coupled to a single cylinder 12 associated with a single mold, or the actuator valve can be fluidly coupled to multiple cylinders 12 associated with multiple molds. A valve toggle can be included for manually opening the actuator valve. Alternatively, an automatic control device can be included for automatically opening the actuator valve.

In an embodiment, the system includes an automatic control device connected to the actuator 6. The automatic control device can include a parison sensor, which detects the presence of a parison between the first mold half 2 and the second mold half 4. The parison sensor can include, for example, a light source that projects a beam of light across a region a parison occupies when a parison is present between the first mold half 2 and the second mold half 4 and a photodetector that can receive the beam of light. The photodetector not detecting the beam of light can be indicative of the presence of the parison; the photodetector detecting the beam of light can be indicative of the absence of the parison. For example, the parison sensor can be connected to control circuitry, which can in turn be connected to a solenoid. The solenoid can be connected to a valve toggle that can open or close an actuator valve.

The system can include a spring 16 connected to a first mold half 2 and connected to a cutting knife 8. The system can include a knife holder 18. The knife holder 18 can be connected to the actuator 6, and the cutting knife 8 can be held by the knife holder 18. For example, the system can include a spring 16 connected to the first mold half 2 and connected to a knife holder 18 that holds the cutting knife 8, as shown in FIGS. 9 and 10. FIG. 9 is a side cross-section, along section B-B of FIG. 7, of a portion of a system for preserving a cutting knife 8, with the cutting knife 8 in the engaged position, shown in top view in FIG. 7. FIG. 10 is a side cross-section, along section D-D of FIG. 8, of a portion of a system for preserving a cutting knife 8, with the cutting knife 8 in the removed position, shown in top view in FIG. 8.

The system can be configured so that the cutting knife 8 is normally in the engaged position. Alternatively, the system can be configured so that the cutting knife 8 is normally in the removed position. Furthermore, the system can be configured so that the actuator 6 is activated, for example, supplied with fluid under pressure, or activated in another manner, when the cutting knife 8 is in the normal position; or the system can be configured so that the actuator 6 is deactivated, for example, not supplied with fluid under pressure, or deactivated in another manner, when the cutting knife 8 is in the normal position.

For example, the embodiment shown in FIGS. 5 and 6 can be configured so that the cutting knife 8 is normally in the engaged position, shown in FIG. 5, when the fluid actuator 36 is normally deactivated, by setting the spring 16, shown in FIG. 9, to be under compression. The force imposed by the spring 16 on the cutting knife 8 can act to maintain the position of the cutting knife 8 when the first mold half 2 and the second mold half 4 move to the closed position, so that the cutting knife 8 properly cuts through the parison material. The fluid actuator 36 shown in FIGS. 5 and 6 can be deactivated when the cylinder space to the left of the piston 14, which can be capable of admitting fluid through an inlet port 32, is not under fluid pressure.

Or, the embodiment shown in FIGS. 5 and 6 can be configured so that the cutting knife 8 is normally in the removed position, shown in FIG. 6, when the fluid actuator 36 is normally activated, by setting the spring 16, shown in FIG. 10, to be under compression. The fluid actuator 36 shown in FIGS. 5 and 6 can be activated when the cylinder space to the left of the piston 14, which can be capable of admitting fluid through the inlet port 32, is under fluid pressure.

In the embodiment shown in FIGS. 5 and 6, the fluid actuator 36 includes a cylinder 12 that admits fluid on a side of the piston 14, so that fluid pressure will act through the piston 14 to force the cutting knife 8 to the removed position; i.e., the cylinder 12 has an inlet port 32 for fluid on the left side of the piston 14. In alternative embodiments, the fluid actuator 36 includes a cylinder 12 that admits fluid on a side of the piston 14, so that fluid pressure will act through the piston 14 to force the cutting knife 8 to the engaged position. The devices shown in FIGS. 5 and 6 could be modified to such an alternative embodiment by, for example, having the inlet port 32 in the cylinder 12 on the right side of the piston 14 and including a link between the rod 30 and the lever 22 so that the piston 14 can pull the lever 22 to the left and thus force the cutting knife 8 to the engaged position. Such an alternative embodiment can be configured so that the cutting knife 8 is normally in the engaged position when the fluid actuator 36 is normally activated, by setting the spring 16 to be under tension. The fluid actuator 36 can be activated when the cylinder space to the right of the piston 14, which can be capable of admitting fluid through an inlet port 32, is under fluid pressure. Or, such an alternative embodiment can be configured so that the cutting knife 8 is normally in the removed position when the fluid actuator 36 is normally deactivated, by setting the spring 16 to be under tension. The fluid actuator 36 can be deactivated when the cylinder space to the right of the piston 14, which can be capable of admitting fluid through an inlet port 32, is not under fluid pressure.

Thus, at least two modes of operation are possible with the embodiment shown in FIGS. 5 and 6. At least two additional modes of operation are possible with an embodiment in which the inlet port 32 is placed to allow fluid to enter to the right of the piston 14 and there is a link between the piston 14 and the lever 22, so that the piston 14 can pull the lever 22 to the left.

For a system for which the cutting knife 8 is normally in the engaged position, as shown in FIG. 5, when the fluid actuator 36 is deactivated, a parison sensor can act to trigger the activation of the fluid actuator 36 when no parison is detected. The fluid actuator 36 can then move the cutting knife 8 to the removed position. And, for example, when the parison sensor later detects the presence of a parison, the parison sensor can act to trigger the deactivation of the fluid actuator 36, so that the cutting knife 8 can return to the engaged position; for example, when the fluid actuator 36 is deactivated, a spring 16 under tension can act to return the cutting knife 8 to the engaged position.

For a system for which the cutting knife 8 is normally in the removed position, as shown in FIG. 6, when the fluid actuator 36 is activated, a parison sensor can act to trigger the deactivation of the fluid actuator 36 when a parison is detected. For a system for which the cutting knife 8 is normally in the engaged position when a fluid actuator 36 is activated, a parison sensor can act to trigger the deactivation of the fluid actuator 36 when no parison is detected. And for a system for which the cutting knife 8 is normally in the removed position when a fluid actuator 36 is deactivated, a parison sensor can act to trigger the activation of the fluid actuator 36 when a parison is detected.

The system can include a fulcrum 20 connected to the first mold half 2; the fulcrum 20 can contact the cutting knife 8 or a knife holder 18 holding the cutting knife 8 during at least part of the motion of the cutting knife 8 from the engaged position to the removed position, as shown in FIGS. 5 and 6. A lever 22 can be connected to the cutting knife 8 or to a knife holder 18 holding the cutting knife 8; a fluid actuator 36 can move the lever 22 to move the cutting knife 8 from the engaged position to the removed position; and a fulcrum 20, connected to the first mold half 2, can contact the lever 22 during at least part of the motion of the cutting knife 8 from the engaged position to the removed position. FIGS. 5 and 6 show an embodiment in which the piston 14 can be driven by a pressurized fluid in the cylinder 12 to move a rod 30; the rod 30 can contact and exert force on a lever 22; the lever 22 can be connected to a knife holder 18 holding a cutting knife 8; and the lever 22, knife holder 18, and cutting knife 8 can tilt about a fulcrum 20 which can contact the knife holder 18.

The fulcrum 20 can be formed from a pin and socket. For example, the fulcrum 20 can include a pin on a knife holder 18, a cutting knife 8, or a lever 22 which fits into a socket on the first mold half 2, or into a socket on a part connected to the first mold half 2. Or, the fulcrum 20 can include a socket or hole in the knife holder 18, the cutting knife 8, or the lever 22 into which a pin protruding from the first mold half 2, or from a part connected to the first mold half 2 fits. Alternatively, a fulcrum can include a portion jutting from the first mold half 2, or from a part connected to the first mold half 2 about which a cutting knife 8, a knife holder 18, or a lever 22 can tilt. Such a jutting portion is not shown in FIG. 5 or 6.

The system for preserving a cutting knife 8 presented herein can be readily adapted to a range of machinery in which a cutting knife cuts material.

A system for self-sharpening a cutting knife can include a first knife connected to a first mold half 2, and a second knife connected to a second mold half 4. The first knife can come into sliding contact with the second knife when the mold halves move from an open position, shown in FIG. 11, to a closed position, shown in FIG. 12. The first knife can be a bed knife, and the second knife can be a cutting knife. Alternatively, as shown in FIGS. 11 and 12, the first knife can be a cutting knife 8, and the second knife can be a bed knife 10. The cutting knife 8 can include a cutting edge 24, and the bed knife can include a sharpening surface 26. In an embodiment, not shown in FIGS. 11 and 12, the bed knife 10 is entirely formed of a sharpening surface 26. The cutting edge 24 can contact and cut a parison when the first mold half 2 and the second mold half 4 move from the open position to the closed position. The sharpening surface 26 can include, for example, a sharpening stone or a monocrystalline diamond coating. The bed knife 10 can include a substrate 28, as shown in FIGS. 11 and 12. The substrate 28 can be, for example, a metal. The cutting edge 24 of the cutting knife 8 and the sharpening surface 26 can be positioned with respect to each other, so that when the first mold half 2 and the second mold half 4 move to the closed position, the cutting edge 24 slides along the sharpening surface 26, so that the sharpening surface 26 sharpens the cutting edge 24. For example, the length of the cutting knife 8 can be positioned at a non-zero angle, e.g., a small angle, with respect to the sharpening surface 26, so that the cutting edge 24 slides along and is sharpened by the sharpening surface 26 when the first mold half 2 and the second mold half 4 move to the closed position.

A force forcing the cutting edge 24 into contact with the bed knife 10 or with a sharpening surface 26 of a bed knife 10 when the cutting knife 8 is in the engaged position and the first mold half 1 and the second mold half 2 move to the closed position can be imposed on the cutting knife 8. Such a force can ensure contact between the cutting edge 24 and the bed knife 10 or the sharpening surface 26 in order to, for example, more effectively cut the parison material and/or ensure sharpening of the cutting edge 24 by the sharpening edge 26. For example, the cutting knife 8 can have a fulcrum, and a spring can be connected to the cutting knife 8 and to the first mold half 2 in order to impose such a force on the cutting knife 8 (not shown in FIGS. 11 and 12). Alternatively, the cutting knife 8 can be held by a knife holder 18; the knife holder 18 can have a fulcrum; and a spring can be connected to the first mold half 2 and to the knife holder 18; so that force is imposed on the cutting knife 8 to force the cutting edge 24 into contact with the sharpening surface 26 when the cutting knife 8 is in the engaged position and the first mold half 2 and the second mold half 4 move to the closed position (not shown in FIGS. 11 and 12).

This system for self-sharpening can prolong the retention of a sharp edge by the cutting edge 24, and thereby increase the period between shut down of the molding apparatus for cutting knife 8 replacement. This system for self-sharpening can be readily adapted to a range of machinery in which a knife cuts material.

The system for self-sharpening can be combined with a system for preserving a cutting knife in which bed knife 10 or the cutting knife 8 can be moved from an engaged position to a removed position. For example, in FIGS. 1-4, the bed knife 10 can include a sharpening surface 26. When the cutting knife 8 is in the engaged position, shown, for example, in FIG. 1, and the first mold half 2 and the second mold half 4 move from the open position, e.g., as shown in FIG. 1, to the closed position, e.g., as shown in FIG. 3, the cutting knife 8 can come into sliding contact with the bed knife 10, and the cutting knife 8 can be sharpened by the bed knife 10.

A method for preserving a cutting knife can include moving a first knife from an engaged position, as shown in FIG. 1, to a removed position, as shown in FIG. 2. In the removed position, the first knife does not contact a second knife when a first mold half 2, to which the first knife is connected, and a second mold half 4, to which the second knife is connected, move from an open position, such as shown in FIG. 2, to a closed position, such as shown in FIG. 4. The first knife can be a bed knife 10 and the second knife can be a cutting knife 8. Alternatively, the first knife can be a cutting knife 8 and the second knife can be a bed knife 10, as shown in FIGS. 1-4.

The method can include triggering an actuator 6 to move the cutting knife 8 from the engaged position, as shown in FIG. 1, to the removed position, as shown in FIG. 2. Triggering an actuator 6 can include activating the actuator 6 to impose force on the cutting knife 8; this can result in the actuator 6 forcing the cutting knife 8 from a normally engaged position, as shown in FIG. 1, to a removed position, as shown in FIG. 2. For example, triggering an actuator 6 can include forcing fluid into a cylinder 12 of a fluid actuator 36, so that the fluid moves a piston 14 within the cylinder 12; and the piston 14, connected to the cutting knife 8, moves the cutting knife 8 from the engaged position to the removed position. For example, a rod 30 can be connected to the piston 14, and the rod 30 can be forced against a lever 22 connected to a knife holder 18 which holds the cutting knife 8. The force imposed by the piston 14 on the knife holder 18 can overcome the force imposed by a spring 16, and move the cutting knife 8 from the engaged position, shown in FIG. 5, to the removed position, shown in FIG. 6. Forcing fluid into the cylinder 12 can include opening an actuator valve connected to the cylinder 12 and for fluidly connecting to a fluid supply.

Or, triggering an actuator 6 can include deactivating the actuator 6 to relieve force on the cutting knife 8; this can result in the actuator 6 allowing the cutting knife 8 to return from a normally engaged position, as shown in FIG. 1, to a removed position, as shown in FIG. 2.

Alternatively, the method can include triggering an actuator 6 to move the cutting knife 8 from a removed position, as shown in FIG. 2, to the engaged position, as shown in FIG. 1. Triggering an actuator 6 can include activating the actuator 6 to impose force on the cutting knife 8; this can result in the actuator 6 forcing the cutting knife 8 from a normally removed position, as shown in FIG. 2, to an engaged position, as shown in FIG. 1.

Or, triggering an actuator 6 can include deactivating the actuator 6 to relieve force on the cutting knife 8; this can result in the actuator 6 allowing the cutting knife 8 to return from a normally removed position, as shown in FIG. 2, to an engaged position, as shown in FIG. 1.

A method for self-sharpening of a cutting knife 8 can include moving a first mold half 2, connected to a first knife, and a second mold half 4, connected to a second knife, from an open position to a closed position. The first knife can be a bed knife 10 and the second knife can be a cutting knife 8. Alternatively, the first knife can be a cutting knife 8 and the second knife can be a bed knife 10, as shown in FIGS. 1 and 3. During the motion of the first mold half 2 and the second mold half 4 from an open position to a closed position, the cutting edge 24 of the cutting knife 8 can slide along a sharpening surface 26 of the bed knife 10. FIG. 11, showing the open position, shows that the cutting edge 24 of the cutting knife 8 can contact the sharpening surface 26 when the first mold half 2 and the second mold half 4 move to the closed position, shown in FIG. 12.

A method for self-sharpening of a cutting knife 8 can include moving the first mold half 2 and the second mold half 4 from the closed position to the open position, so that the cutting edge 24 slides along the sharpening surface 26. This sliding during moving from the closed position to the open position can create a sharp burr on the cutting edge 24. This sharp burr can be advantageous, because it can act to cut a parison when the first mold half 2 and the second mold half 4 move from the open position to the closed position. For example, the first mold half 2 and second mold half 4, shown in the closed position in FIG. 12, can move to the open position shown in FIG. 11.

The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. All examples presented are representative and non-limiting. The above-described embodiments of the invention may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described. 

1. A system for preserving a cutting knife, comprising: a first mold half and a second mold half; an actuator connected to the first mold half; a first knife connected to the actuator; a second knife connected to the second mold half; wherein the first mold half and the second mold half have an open position and a closed position; wherein the actuator moves the first knife from an engaged position to a removed position at which the first knife does not contact the second knife when the mold halves move from the open position to the closed position.
 2. The system of claim 1, wherein the first knife is a bed knife, and the second knife is a cutting knife.
 3. The system of claim 1, wherein the first knife is a cutting knife, and the second knife is a bed knife.
 4. The system of claim 3, wherein the actuator comprises a cylinder capable of admitting a fluid for fluid coupling to a fluid supply and a piston within the cylinder and wherein the piston is connected to the cutting knife.
 5. The system of claim 4, wherein the fluid is a gas.
 6. The system of claim 4, further comprising an actuator valve fluidly coupled to the cylinder and for fluidly coupling to the fluid supply.
 7. The system of claim 6, further comprising a valve toggle for manually opening the actuator valve.
 8. The system of claim 6, further comprising an automatic control device for automatically opening the actuator valve.
 9. The system of claim 3, further comprising an automatic control device connected to the actuator, wherein the automatic control device comprises a parison sensor.
 10. The system of claim 3, further comprising a spring connected to the cutting knife and connected to the first mold half.
 11. The system of claim 3, further comprising a knife holder, wherein the knife holder is connected to the actuator and the cutting knife is held by the knife holder.
 12. The system of claim 3, further comprising: a fulcrum connected to the first mold half; and a knife holder, wherein the cutting knife is held by the knife holder and the fulcrum contacts the knife holder during at least part of the motion of the cutting knife from the engaged position to the removed position.
 13. The system of claim 3, further comprising: a fulcrum connected to the first mold half; a lever connected to the cutting knife; wherein the actuator moves the lever to move the cutting knife from the engaged position to the removed position and wherein the fulcrum contacts the lever during at least part of the motion of the cutting knife from the engaged position to the removed position.
 14. The system of claim 3, wherein the cutting knife comprises a cutting edge and the bed knife comprises a sharpening surface.
 15. A system for self-sharpening a cutting knife, comprising: a first mold half and a second mold half; a first knife connected to the first mold half; and a second knife connected to the second mold half, wherein the first mold half and the second mold half have an open position and a closed position, the first knife comes into sliding contact with the second knife when the mold halves move from the open position to the closed position, the first knife is a cutting knife and the second knife is a bed knife, and the cutting knife comprises a cutting edge and the bed knife comprises a sharpening surface.
 16. The system of claim 15, wherein the sharpening surface comprises a sharpening stone.
 17. The system of claim 15, wherein the sharpening surface comprises a monocrystalline diamond coating.
 18. The system of claim 15, the bed knife further comprising a substrate, wherein the substrate is a metal.
 19. The system of claim 15, wherein the cutting knife has a length and the length of the cutting knife is positioned at a non-zero angle with respect to the sharpening surface, so that the cutting edge slides along the sharpening surface when the mold halves move to the closed position.
 20. A method for preserving a cutting knife, comprising moving a first knife from an engaged position to a removed position at which the first knife does not contact a second knife when a first mold half to which the first knife is connected and a second mold half to which the second knife is connected move from an open position to a closed position.
 21. The method of claim 20, the moving a first knife comprising triggering an actuator to move the first knife from the engaged position to the removed position, wherein the first knife is a cutting knife, and the second knife is a bed knife.
 22. The method of claim 21, the triggering an actuator comprising deactivating the actuator to relieve force on the cutting knife.
 23. The method of claim 21, the triggering an actuator comprising activating the actuator to impose force on the cutting knife.
 24. The method of claim 23, the triggering an actuator comprising forcing a fluid into a cylinder of a fluid actuator, so that the fluid moves a piston within the cylinder, wherein the piston is connected to the cutting knife, and the piston moves the cutting knife from the engaged position to the removed position.
 25. A method for self-sharpening of a cutting knife, comprising moving a first mold half connected to a first knife and a second mold half connected to a second knife from an open position to a closed position, wherein the first knife is a bed knife and the second knife is a cutting knife or the first knife is a cutting knife and the second knife is a bed knife, and a cutting edge of the cutting knife slides along a sharpening surface of the bed knife.
 26. The method of claim 25, further comprising moving the first mold half and the second mold half from the closed position to the open position, so that the cutting edge slides along the sharpening surface to create a sharp burr on the cutting edge. 